1. Technical Field
This invention relates to a position indicator that is used together with a position detecting device and that has, e.g., a pen shape, and particularly to a position indicator having a writing pressure detection function to detect pressure applied to the tip part of the position indicator.
2. Description of the Related Art
As an input device for a personal computer and so forth, a position input device is known that uses a position detecting device that has an input surface, on which pointing operation and input of characters, figures, etc. are performed, and that detects the operation input position on the input surface by the electromagnetic induction system. Normally, for this kind of position input device, a position indicator that has a pen-like shape and includes a writing pressure detector is used as an operation input means for the input surface of the position detecting device.
As the writing pressure detector of this position indicator, e.g., a capacitance-variable capacitor like that described in Patent Document 1 (Japanese Patent Laid-open No. Hei 4-96212) is used. The capacitance-variable capacitor described in this Patent Document 1 has a first electrode attached to one surface (hereinafter the “one surface”) of a dielectric and a second electrode, which has flexibility and is disposed on the side of the other surface (hereinafter the “other surface”) of the dielectric opposite to the one surface, as mechanical structural parts housed in an elongated tubular housing. Furthermore, the capacitance-variable capacitor includes a spacer means that separates the second electrode from the other surface of the dielectric by a slight gap except for a partial area, and includes a part that applies relative pressure or causes displacement between the second electrode and the dielectric. The part that applies the relative pressure or causes displacement is coupled to a core body of the position indicator having a pen shape. When a writing pressure is applied to the position indicator from one end part of its housing, the flexible second electrode is displaced due to axial-directional force applied to the core body. Thereby, the distance between the first electrode and the second electrode opposed to each other with the intermediary of the dielectric changes and the capacitance changes.
Therefore, the capacitance-variable capacitor of the position indicator in Patent Document 1 has a large number of parts—specifically, the dielectric, first electrode, second electrode, spacer, elastic body, holder to hold the dielectric, terminal members for connection between the first and second electrodes and a printed wiring board, and so forth—and these parts are separate mechanical parts. This causes a problem that the configuration of the position indicator is complicated and assembling of the position indicator takes a lot of labor hours and high cost.
On the other hand, capacitive pressure sensors fabricated by a semiconductor microfabrication technique typified by, e.g., MEMS (Micro Electro Mechanical System) technique have been proposed as disclosed in Patent Document 2 (Japanese Patent Laid-open No. Hei 11-284204), Patent Document 3 (Japanese Patent Laid-open No. 2001-83030), Patent Document 4 (Japanese Patent Laid-open No. 2004-309282), and Patent Document 5 (U.S. Published Application No. 2002/0194919), for example.
The pressure sensors disclosed in Patent Document 2 to Patent Document 5 have a semiconductor structure including a first electrode and a second electrode disposed opposite to the first electrode at a predetermined distance. The distance between the first electrode and the second electrode changes depending on the pressure applied to the first electrode. Thereby, the capacitance formed between the first electrode and the second electrode changes. Thus, the pressure can be detected as a change in the capacitance.